Wireless devices can now handle voice and/or data, allowing simplex and/or duplex voice calls, video calls, text messaging, and internet browsing. Some wireless communication devices can now handle voice-over-internet-protocol (VoIP) calls, and others are able to handle multimedia (voice, video, graphics) calls through wireless networks and/or through wireless networks connected to the internet or media servers.
Different types of calls, initiated by wireless devices, can be restricted for some or most of their outgoing traffic; for example voice and data calls, as well as internet web browsing, can be restricted to those call tariffs made available by the wireless network(s) that is subscribed to. Those wireless networks could be operated by traditional wireless network operators or so called virtual network operators. The restrictions can even limit which web servers the user is actually allowed to access. In most or all cases the restrictions will limit the users in their home country to only one wireless network, i.e. the home wireless network to which the user is subscribed to.
Users of wireless devices subscribed to a specific wireless network in their home country, may however wish to have a choice of call set-up route(s), and also have the choice of viewing any web server or web-page that they desire, and to initiate their outgoing calls at the tariff of their choice and through any of the wireless network(s) available in their home country as well as when roaming abroad. This would give each wireless device user the freedom to choose the cheapest option for each call set-up route for any outgoing traffic, such as outgoing -SMS, -voice call, -data call.
There are several ways of achieving this, but all have drawbacks.
It is known to provide a wireless device (e.g. a mobile telephone) with 2 separate SIMs, each associated with a different network operator; the 2 separate SIMs sometimes need to be cut down to fit a single SIM reader, or else a special carrier for two SIMs is provided that itself connects to a conventional SIM package. These devices are sometimes called ‘ghost SIMs’. So, for example, a person who frequently travels between the UK and the US would have a single mobile telephone that he could use in both countries, fitted with a dual SIM ‘ghost’. If his home mobile operator is based in the UK, he would normally pay roaming charges when he makes calls from the US; call costs can be 10× greater from the US because of this. But with a dual SIM ‘ghost’ on his mobile telephone, the user can toggle between SIMs by repeatedly turning the device off/on. So he can use a SIM from a US operator when in the US and a SIM from a UK operator when in the UK. But that means that incoming calls to the UK telephone number will go unanswered when the US SIM is being used, and vice versa, which is inconvenient. The user could simply toggle the phone to the US SIM only when he needs to make a call from the US, and then remember to toggle back afterwards. But that is inconvenient. And the user also has to obtain the 2 separate SIMs in the first place, which can again be inconvenient.
He could alternatively keep 2 different mobile telephones, one for use in the UK and one for the US, with each associated with a UK and US operator respectively. Then, no roaming charges will be paid when he calls from the US, because he uses the mobile telephone associated with the US operator. But having 2 different mobile telephones is costly and inconvenient, especially as people will no doubt call him on his UK mobile telephone number when he is in the US, so he would need to have both devices constantly at hand when traveling in the US.
Another solution is to have a conventional mobile telephone using just a single SIM, but to have 2 different SIMs, and to physically swap the SIM from a UK operator into the device when in the UK, and swap in a SIM from a US operator when in the US. But that is very inconvenient, and can mean that calls to the UK telephone number will just divert to voicemail when the US SIM is in use, and vice versa when the UK SIM is in use.
Before summarising the invention, we will explain some background terms. The IMSI is a unique non-dialable number allocated to each mobile subscriber that identifies the subscriber and his or her operator subscription. The IMSI is stored in the Subscriber Identity Module (SIM). The IMSI is made up of three parts (1) the mobile country code (MCC) consisting of three digits, (2) the Mobile Network Code (MNC) consisting of two digits, and (3) the Mobile Subscriber Identity Number (MSIN) with up to 10 digits.
A Home Location Register (HLR) is a database that contains mobile subscriber information for all subscribers to an operator. A Visitor Location Register (VLR) is a database owned and maintained by a mobile operator. It contains temporary information about mobile subscribers that are currently located in a geographic area served by that mobile operator, but whose Home Location Register (HLR) is elsewhere.
HLR subscriber information includes the International Mobile Subscriber Identity (IMSI), service subscription information, location information (the identity of the currently serving Visitor Location Register (VLR) to enable the routing of mobile-terminated calls), service restrictions and supplementary services information. The HLR also initiates transactions with VLRs to complete incoming calls and to update subscriber data.
When a mobile subscriber roams away from his home location and into a remote location (typically to a different country), SS7 messages are used to obtain information about the subscriber from the HLR, and to create a temporary record for the subscriber in the VLR. There is usually one VLR per operator. The VLR automatically updates the HLR with the new location information, which it does using an SS7 Location Update Request Message. The Location Update Message is routed to the HLR through the SS7 network, based on the global title translation of the IMSI that is stored within the SCCP Called Party Address portion of the message. The HLR responds with a message that informs the VLR whether the subscriber should be provided service in the new location.